This invention relates to containment systems and more particularly containment systems for use in the semiconductor processing industry comprising plastic drums with ports and fitting assemblages for connecting to/or closing said ports.
Blow molded thermoplastic drums have replaced steel drums in many applications. Particularly in the semiconductor processing industry, the chemicals to be contained are highly pure, react with, and are contaminated by contact with metals. Such drums are typically blow molded of high density polyethylene. It is appropriate to eliminate any additives in the polyethylene (PE) which contacts the fluid in the drum and the fitting assemblages system since such additives may diffuse into the highly pure chemicals and contaminate same. Such drums are subject to Department of Transportation regulations which require that the exterior of the drum has ultraviolet inhibitors to prevent or minimize the degradation of the drum. The need to have additives in the PE at the exterior of the drum and the need to have highly pure PE on the interior fluid contacting surfaces has been addressed by the use of a multiple layered parison during the blow molding of the drums.
Known plastic drum containment systems for use in containing and dispensing highly pure chemicals have been structurally complex with numerous seals and therefore are relatively expensive. The expense often dictates that the system components must be used multiple times rather than allowing a single use. The complexity is due in part to the need to provide port connections and closures of very high integrity while overcoming the deficiencies in the blow molding process. These deficiencies relate primarily to the high tolerances inherent in the formation of threaded surfaces and sealing surfaces at the port during the blow molding process. Conventionally the systems will utilize interior threads on the drum neck which are formed during the blow molding process. Secondary fittings will threadingly engage with the neck and will trap and axially compress sealing rings between the secondary fitting and the top edge or at least an upwardly facing surface of the neck. The injection molded secondary fitting will then provide appropriate precision threaded surfaces and sealing surfaces for attachment of closures or dispense heads. See, for example, U.S. Pat. Nos. 5,526,956; 5,511,692; 5,667,253; 5,636,769; and 5,108,015. Conventionally, such connections between the secondary fitting and closure or dispense head will use axially loaded o-rings. In containment systems as such, axially loaded o-rings tend to need replacement more frequently than desired and tightening torques of the dispense heads and closures are more critical than desirable. A sealing system is needed that provides longer lasting o-rings and less critical tightening torque requirements.
Moreover, these secondary fittings typically require significant annular space in that they are in engagement with the inside threads of the neck of the drum port. This use of space restricts the space available for flow ducts. Additionally, the inside threads are difficult to clean.
Such containment systems may utilize dispense heads and down tube assembles for withdrawal by suction of the chemicals in the drums. Conventionally, such dispense heads and down tube assemblies are structurally complex, have several sealing surfaces, and thus are required to be precisely molded or machined. A containment system is needed that utilizes a simplified dispense head and down tube assembly each with a minimal number of sealing surfaces.
A simple containment system is needed that provides sealing and connection surfaces for closures and dispense heads for high purity chemicals such as used in the semiconductor processing industry. Such a system should have structurally simple components, a minimal number of o-rings, and provide connections and closures of high integrity.
Closures for such ports may or not be vented and may have valves for discharging pressure buildup in the drum. Such closures typically are formed of multiple components with exteriorly exposed openings, perforations, tool recesses, and interfaces between the components. Such openings, interfaces, recesses, and perforations may operate as collection points for impurities, contaminants, the contents of the drum, or other matter. Additionally such openings, perforations, and interfaces provide a pathway for leakage of the contents of the drum or for entry of contaminants into the interior of the drum. A closure is needed that has the minimal number of perforations, vents, and interfaces between components. Ideally, such a closure will have a smooth outer shell completely covering the neck without any exposed perforations, openings, or interfaces between components of the closure.
Moreover, a closure sealing directly with the inside threads, such as a plug, as opposed to a closure on a secondary fitting, will require tightening said plug directly and the requirement that the closure does not have UV inhibiting additives in contact with the drum contents necessitates that the exterior of the plug also be free of UV inhibitors which is not an ideal situation. A closure is needed in which the component part that is being tightened with the threads on the neck is not the component part which is sealing the neck opening and which is exposed to the contents of the drum.